Investigation of interfacial microstructure and mechanical performance within TiAl to Ti2AlNb alloy vacuum diffusion bonded joints

This research focuses on the effect of bonding temperature and holding time on the interfacial microstructure, mechanical performance and fracture behavior of diffusion bonded TiAl and Ti2AlNb intermetallic alloys. Under the pressure of 20 MPa, various bonding temperatures and holding times were explored and the optimized bonding parameter was determined to be 975 degrees C/60 min. Along with the changing of bonding parameters, the bonding defect, elemental distribution, microstructural evolution, micro-nano mechanics and corresponding mechanical properties of bonded joints were investigated. The findings indicated that the reaction zone was composed of three distinct interfacial layers, that is, a dark gray alpha 2 layer next to TiAl alloy, a light gray alpha 2 layer with Al(Nb, Ti)2 particles distributing between layer II and layer III, and a B2 + O mixed layer adjacent Ti2AlNb alloy. The maximum elastic modulus of 205 GPa was measured in the alpha 2 phase on the Ti2AlNb side, whereas the Al(Nb, Ti)2 particles exhibited the highest nano-hardness of 14.5 GPa. By optimizing the bonding parameters, a subtle suture structure between layers I and II and well-distributed Al(Nb, Ti)2 particles were regulated at the bonding interface, which endowed the resultant joint at 975 degrees C for 60 min with shear strength of 319 MPa. The subtle suture structure between layer I and layer II effectively prevented the propagation of fracture, while the fine Al(Nb, Ti)2 particles alleviated the stress concentration at the bonding interface. Furthermore, crack bridging and crack blunting also enhanced the mechanical performance of the joint. The results in this paper provide a promising approach for addressing the challenge of joining dissimilar intermetallic alloys.